Deterministic Decomposition of the Unsteady Flow in a Unidirectional Axial Turbine for OWC Plant

2018 ◽  
Author(s):  
Nuria Alvarez Bertrand ◽  
Jesús Manuel Fernández Oro ◽  
Bruno Pereiras García ◽  
Manuel García Díaz
Keyword(s):  
Flow Rate ◽  
High Efficiency ◽  
Low Flow ◽  
Oscillating Water Column ◽  
Turbine Stage ◽  
Flow Rates ◽  
Aerodynamic Efficiency ◽  
Axial Turbine ◽  
Deterministic Framework ◽  
Energy Plants

The “twin-turbine” configuration has recently emerged as a feasible possibility for unidirectional turbines to be introduced in Oscillating Water Column wave energy plants without requiring auxiliary rectifying systems. Previous investigations by the authors have been focused on the development of a numerical CFD model to analyze the performance of a unidirectional axial turbine for twin turbine configuration in an OWC system. In this paper, all these numerical databases are further post-processed using a deterministic framework to give more insight about the flow patterns within the turbine. The final objective is the analysis of the unsteady features of the flow and the stator-rotor interactions using a deterministic decomposition. The present study reveals that levels of deterministic unsteadiness in the inter-row region are moderate, being more intense as the flow rate is decreased. Turbulence intensities are also observed to be clearly prominent in case of lower flow rates. Although these findings appear to be contradictory with the high-efficiency low flow rates of the turbine, the major levels of stator-rotor unsteadiness at higher flow rates (shown by the deterministic decomposition) justify the serious penalty in the aerodynamic efficiency as the turbine flow rate is increased. Finally, some advices with respect the design of the vane row in the turbine stage are given to control the generation of turbulence and stator-rotor interaction.

Experimental Study of Ingestion in the Rotor-Stator Disk Cavity of a Subscale Axial Turbine Stage

2014 ◽  
Author(s):  
J. Balasubramanian ◽  
P. S. Pathak ◽  
J. K. Thiagarajan ◽  
P. Singh ◽  
R. P. Roy ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Discharge Coefficient ◽  
Computational Effort ◽  
Radial Clearance ◽  
Turbine Stage ◽  
Flow Rates ◽  
Axial Turbine ◽  
Discharge Coefficients ◽  
Purge Flow

While it is widely recognized that ingestion of hot gas from the main annulus of axial gas turbine stages into rotor-stator disk cavities depend strongly on the unsteadiness of the prevailing flow field, the large computational effort needed to simulate the flow field renders its use in the design of turbine internal air system and seals difficult. As an alternative, considerable effort has been devoted in recent years to develop simple orifice models of disk cavity rim seals based on time-averaged flow information; these models contain empirical discharge coefficients for ingestion into and egress from the cavities. The present experimental work in a subscale axial turbine stage reports a simple orifice model of an axially-overlapping radial-clearance seal at the disk cavity rim and values of the discharge coefficients over a range of purge flow rate supplied to the cavity. In the experiments, the ingestion process was dominated by the main gas annulus flow. Time-averaged static pressure distribution was measured in the main annulus and in the disk cavity; the driving force for ingestion and egress was taken to be the pressure differential between the main annulus and the rim cavity at prescribed locations. Time-averaged ingestion was measured using the tracer gas technique; the pressure and ingestion data were combined to obtain the ingestion and egress discharge coefficients at several purge flow rates. The location on the vane platform 1mm upstream of its lip represented the main gas annulus pressure in the calculation of discharge coefficients. In the rim cavity, two locations on the stator, one in the ‘seal region’ and the other slightly inward radially, were prescribed to represent the rim cavity pressure as well as the sealing effectiveness. Two corresponding sets of ingestion and egress discharge coefficients are reported for the various purge flow rates. The ingestion discharge coefficient obtained using the seal region location in the rim cavity decreased as the purge flow rate increased; the corresponding egress discharge coefficient increased with purge flow rate. For the rim cavity location slightly inward radially from the seal region, the egress discharge coefficient maintained the same trend; however, the ingestion discharge coefficient decreased only slightly as the purge flow rate increased. It is suggested that the seal region location in the rim cavity is the more appropriate location in calculating the rim seal discharge coefficients. The ratio of ingestion to egress discharge coefficients exhibited considerable variation with purge flow rate.

scholarly journals Effects of Soil Conservation Practices on Sediment Yield from Forest Road Ditches in Northern Iran

2020 ◽  
Vol 41 (2) ◽  
pp. 299-308
Author(s):  
Rasoul Khandouzi ◽  
Aidin Parsakhoo ◽  
Vahedberdi Sheikh ◽  
Aliakbar Mohamadali Pourmalekshah
Keyword(s):  
Flow Rate ◽  
Sediment Yield ◽  
Festuca Arundinacea ◽  
High Efficiency ◽  
Sediment Concentration ◽  
Low Flow ◽  
Road Maintenance ◽  
Northern Iran ◽  
Flow Rates ◽  
Forest Road

The fine-textured soil in forest road ditches is very susceptible to water erosion especially in rainy seasons in Hyrcanian forest. This study examined the yield of ditch segment-scale sediment after releasing two flow rates of 5 l s-1 and 10 l s-1 in segments treated by riprap (RR), grass cover by Festuca arundinacea L. (GC), compacted cotton geotextile (CG) and wooden wattle by local slash (WW). Sediment sampling from the runoff was carried out at the end of each segment every minute. Runoff flow velocity in different treatments was measured using an electromagnetic flow meter. Sediment concentration and runoff velocity in treatments of RR, GC, CG, WW was significantly lower than that of the control plot (Ctl). Increasing flow rate from 5 l s-1 to 10 l s-1 caused no significant change in sediment concentration (except for Ctl and RR) and runoff velocity (except for Ctl and CG), which means that some water might have penetrated into treated soil by RR, GC and WW and this is not acceptable in forest road maintenance practices. Sediment yield from RR (0.36 g l-1) and Ctl (0.50 g l-1) under the flow rate of 10 l s-1 was significantly higher than that of 5 l s-1 with values of 0.21 g l-1 and 0.38 g l-1, respectively. Minimum amount of sediment concentration was observed for CG (0.20 g l-1) with compacted ditch bed. Moreover, runoff velocity in CG and Ctl under the flow rate of 10 l s-1 was significantly higher than that of 5 l s-1. For a forest road with dimension 30×50 cm, slope of 5%, and clay soil with porosity of 57%, treatments of compacted CG can be used in ditch with low flow rates (5 l s-1) and high flow rate (10 l s-1) because of their high efficiency in reducing sediment yield.

Assessment of the Use of Humidified Nasal Cannulas for Oxygen Therapy in Patients with Epistaxis

ORL ◽  
2021 ◽  
pp. 1-5
Author(s):  
Jingjing Liu ◽  
Tengfang Chen ◽  
Zhenggang Lv ◽  
Dezhong Wu
Keyword(s):  
Flow Rate ◽  
Oxygen Therapy ◽  
Preliminary Investigation ◽  
Nasal Cannula ◽  
Low Flow ◽  
Antiplatelet Drugs ◽  
Flow Rates ◽  
The Past ◽  
Oxygen Inhalation ◽  
Significant Difference

<b><i>Introduction:</i></b> In China, nasal cannula oxygen therapy is typically humidified. However, it is difficult to decide whether to suspend nasal cannula oxygen inhalation after the nosebleed has temporarily stopped. Therefore, we conducted a preliminary investigation on whether the use of humidified nasal cannulas in our hospital increases the incidence of epistaxis. <b><i>Methods:</i></b> We conducted a survey of 176,058 inpatients in our hospital and other city branches of our hospital over the past 3 years and obtained information concerning their use of humidified nasal cannulas for oxygen inhalation, nonhumidified nasal cannulas, anticoagulant and antiplatelet drugs, and oxygen inhalation flow rates. This information was compared with the data collected at consultation for epistaxis during these 3 years. <b><i>Results:</i></b> No significant difference was found between inpatients with humidified nasal cannulas and those without nasal cannula oxygen therapy in the incidence of consultations due to epistaxis (χ<sup>2</sup> = 1.007, <i>p</i> &#x3e; 0.05). The same trend was observed among hospitalized patients using anticoagulant and antiplatelet drugs (χ<sup>2</sup> = 2.082, <i>p</i> &#x3e; 0.05). Among the patients with an inhaled oxygen flow rate ≥5 L/min, the incidence of ear-nose-throat (ENT) consultations due to epistaxis was 0. No statistically significant difference was found between inpatients with a humidified oxygen inhalation flow rate &#x3c;5 L/min and those without nasal cannula oxygen therapy in the incidence of ENT consultations due to epistaxis (χ<sup>2</sup> = 0.838, <i>p</i> &#x3e; 0.05). A statistically significant difference was observed in the incidence of ENT consultations due to epistaxis between the low-flow nonhumidified nasal cannula and nonnasal cannula oxygen inhalation groups (χ<sup>2</sup> = 18.428, <i>p</i> &#x3c; 0.001). The same trend was observed between the 2 groups of low-flow humidified and low-flow nonhumidified nasal cannula oxygen inhalation (χ<sup>2</sup> = 26.194, <i>p</i> &#x3c; 0.001). <b><i>Discussion/Conclusion:</i></b> Neither high-flow humidified nasal cannula oxygen inhalation nor low-flow humidified nasal cannula oxygen inhalation will increase the incidence of recurrent or serious epistaxis complications; the same trend was observed for patients who use anticoagulant and antiplatelet drugs. Humidification during low-flow nasal cannula oxygen inhalation can prevent severe and repeated epistaxis to a certain extent.

Simulation on Linear-Motor-Driven Water Hydraulic Reciprocating Plunger Pump

2013 ◽  
Vol 842 ◽  
pp. 530-535 ◽  
Author(s):  
Zeng Meng Zhang ◽  
Yong Jun Gong ◽  
Jiao Yi Hou ◽  
Han Peng Wu
Keyword(s):  
Flow Rate ◽  
Deep Sea ◽  
High Efficiency ◽  
Control Method ◽  
Sea Water ◽  
Linear Motor ◽  
Low Flow ◽  
Flow Pulsation ◽  
Plunger Pump ◽  
Water Hydraulic

The water hydraulic reciprocating plunger pump driven by linear motor is suitable to deep sea application with high efficiency and variable control. Aiming to study the principle structure and working characteristics of the pump, two patterns of valve and piston distribution were designed. And the control method and the performance were analyzed by simulation based on the AMESim model. The results show that the pressure and flow pulsation of piston type pump are much smaller than the valve type, even though the piston type is large in scale and works at low flow rate. Compared with a valve distribution tri-linear-motor reciprocating plunger pump (VDTLMP), as the flow rate of the piston distribution double linear motor reciprocating plunger pump (PDDLMP) is decreased from 36.7 L/min to 21.2 L/min theoretically, the pressure pulsation amplitude is decreased from 46% to 2%, and the flow pulsation rate is also decreased from 0.266 to 0.007. These results contribute to the research on deep-sea water hydraulic power pack and direct drive pump with high efficiency and energy conservation.

Experimental Investigation of Pressure Fluctuations on Inner Wall of a Centrifugal Pump

2019 ◽  
Vol 36 (4) ◽  
pp. 401-410 ◽  
Author(s):  
Xiao-Qi Jia ◽  
Bao-Ling Cui ◽  
Zu-Chao Zhu ◽  
Yu-Liang Zhang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
High Flow ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Pressure Distributions ◽  
Blade Passing Frequency

Abstract Affected by rotor–stator interaction and unstable inner flow, asymmetric pressure distributions and pressure fluctuations cannot be avoided in centrifugal pumps. To study the pressure distributions on volute and front casing walls, dynamic pressure tests are carried out on a centrifugal pump. Frequency spectrum analysis of pressure fluctuation is presented based on Fast Fourier transform and steady pressure distribution is obtained based on time-average method. The results show that amplitudes of pressure fluctuation and blade-passing frequency are sensitive to the flow rate. At low flow rates, high-pressure region and large pressure gradients near the volute tongue are observed, and the main factors contributing to the pressure fluctuation are fluctuations in blade-passing frequency and high-frequency fluctuations. By contrast, at high flow rates, fluctuations of rotating-frequency and low frequencies are the main contributors to pressure fluctuation. Moreover, at low flow rates, pressure near volute tongue increases rapidly at first and thereafter increases slowly, whereas at high flow rates, pressure decreases sharply. Asymmetries are observed in the pressure distributions on both volute and front casing walls. With increasing of flow rate, both asymmetries in the pressure distributions and magnitude of the pressure decrease.

Effects of short blades on performance and inner flow characteristics of a low-specific-speed centrifugal pump

2017 ◽  
Vol 231 (4) ◽  
pp. 290-302 ◽  
Author(s):  
Can Kang ◽  
Ning Mao ◽  
Chen Pan ◽  
Yang Zhu ◽  
Bing Li
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Low Flow ◽  
Back Surface ◽  
Flow Rates ◽  
Pump Operation ◽  
Low Specific Speed ◽  
Specific Speed

A low-specific-speed centrifugal pump equipped with long and short blades is studied. Emphasis is placed on the pump performance and inner flow characteristics at low flow rates. Each short blade is intentionally shifted towards the back surface of the neighboring long blade, and the outlet parts of the short blades are uniformly shortened. Unsteady numerical simulation is conducted to disclose inner flow patterns associated with the modified design. Thereby, a comparison is enabled between the two schemes featured by different short blades. Both practical operation data and numerical results support that the deviation and cutting of the short blades can eliminate the positive slope of pump head curve at low flow rates. Therefore, the modification of short blades improves the pump operation stability. Due to the shortening of the outlet parts of the short blades, velocity distributions between impeller outlet and radial diffuser inlet exhibit explicitly altered circumferential flow periodicity. Pressure fluctuations in the radial diffuser are complex in terms of diversified periodicity and amplitudes. Flow rate influences pressure fluctuations in the radial diffuser considerably. As flow rate decreases, the regularity of the orbit of hydraulic loads exerted upon the impeller collapses while hydraulic loads exerted upon the short blades remain circumferentially periodic.

Numerical Studies on the Effect of Tip Clearance and Tip Cooling Flow on Endwall Losses of an Unshrouded Axial Turbine Rotor

2013 ◽  
Author(s):  
K. Asgar Ali ◽  
Quamber H. Nagpurwala ◽  
Abdul Nassar ◽  
S. V. Ramanamurthy
Keyword(s):  
Flow Rate ◽  
Layer Growth ◽  
Coolant Flow ◽  
Tip Clearance ◽  
Coolant Flow Rate ◽  
Total Efficiency ◽  
Turbine Stage ◽  
Suction Surface ◽  
Axial Turbine ◽  
Ejection Rate

This paper deals with the numerical investigations on a low pressure axial turbine stage to assess the effect of variation in rotor tip clearance and tip coolant ejection rate on the end wall losses. The rotor, along with the NGV, was modeled to represent the entire turbine stage. The CFX TASCflow software was used to perform steady state analysis for different rotor tip clearances and different tip coolant ejection rates. The locations of the cooling slots were identified on the blade tip and the coolant ejection rate was specified at these areas. The simulations were carried out with tip clearances of 0%, 1% and 2% of blade height and ejection flow rates of 0.5%, 0.75% and 1% of main turbine flow rate. It is shown that the size and strength of the leakage vortex is directly related to the tip clearance. The reduction in efficiency is not in linearity with the tip clearance owing to the effect of boundary layer growth on the end walls. Introduction of the tip coolant flow shows increased total–total efficiency compared to that of the uncooled tip. This is attributed to a reduction in the strength of the leakage vortex due to reduced cross-flow over the tip clearance from pressure surface to suction surface. At a coolant flow rate of 0.75% of the main flow rate, there is significant increase in efficiency of about 0.5%. Optimum tip clearance and coolant flow rate are obtained based on the results of the present analysis.

Cerebral Hyperperfusion Syndrome by the Numbers: Transient Focal Neurological Deficit, Imaging-Proven Focal Hyperperfusion, and High Graft Flow Rate Following Superficial Temporal Artery-Middle Cerebral Artery bypass in a Patient With Symptomatic Carotid Occlusion—Case Report

2018 ◽  
Vol 15 (6) ◽  
pp. E94-E99 ◽  
Author(s):  
Ralph Rahme ◽  
Tejaswi D Sudhakar ◽  
Marjan Alimi ◽  
Timothy G White ◽  
Rafael A Ortiz ◽  
...  
Keyword(s):  
Middle Cerebral Artery ◽  
Flow Rate ◽  
Perfusion Imaging ◽  
Superficial Temporal Artery ◽  
Temporal Artery ◽  
Low Flow ◽  
Flow Rates ◽  
Cerebral Hyperperfusion Syndrome ◽  
Cerebral Hyperperfusion ◽  
Graft Flow

Abstract BACKGROUND AND IMPORTANCE Cerebral hyperperfusion syndrome (CHS) is a well-known complication of superficial temporal artery (STA) to middle cerebral artery (MCA) bypass for ischemic cerebrovascular disease. While this argues against “low flow” in the bypass construct, flow rates in the graft have not been previously quantified in the setting of CHS. CLINICAL PRESENTATION A 58-yr-old man presented with recurrent left hemispheric ischemic strokes and fluctuating right hemiparesis and aphasia. Vascular imaging revealed left cervical internal carotid artery occlusion and perfusion imaging confirmed left hemispheric hypoperfusion. After failing to respond to maximal medical therapy, the patient underwent single-barrel STA-MCA bypass. Postoperatively, his symptoms resolved and blood pressure (BP) was strictly controlled within normal range. However, 2 d later, he developed severe expressive aphasia. CTA demonstrated a patent bypass graft and SPECT showed focal hyperperfusion in Broca's speech area. Seizure activity was ruled out. A high graft flow rate of 52 mL/min was documented by quantitative magnetic resonance angiography (MRA). Thus, the diagnosis of CHS was made and managed with strict BP control. The patient exhibited complete recovery of speech over a period of days and was discharged home. Repeat SPECT at 4 mo showed resolution of hyperperfusion and quantitative MRA demonstrated reduction of graft flow rate to 34 mL/min. CONCLUSION This is the first case of perfusion imaging-proven CHS after STA-MCA bypass, where high graft flow rates are objectively documented. Our observations constitute irrefutable evidence challenging the classic belief that the STA-MCA bypass is a low-flow construct.

Interaction between CO2 concentration and flow rate on peripheral airway resistance

1991 ◽  
Vol 70 (6) ◽  
pp. 2514-2521 ◽  
Author(s):  
A. Kaise ◽  
A. N. Freed ◽  
W. Mitzner
Keyword(s):  
Flow Rate ◽  
Airway Resistance ◽  
Co2 Concentration ◽  
Low Flow ◽  
Flow Rates ◽  
Peripheral Airway ◽  
Residual Capacity ◽  
Local Ventilation ◽  
End Tidal ◽  
The Relationship

In the present study, we investigated the interaction between CO2 concentration and rate of delivered flow on peripheral airway resistance (Rp) in the intact canine lung. Dogs were anesthetized, intubated, paralyzed, and mechanically ventilated with room air to maintain end-tidal CO2 between 4.8 and 5.2%. Using a wedged bronchoscope technique, we measured Rp at functional residual capacity. The relationship between CO2 concentration and Rp was measured at flow rates of 100 and 400 ml/min with 5, 3, 2, 1, and 0% CO2 in air. Measurements were made at the end of a 3-min exposure to each gas. At low flow rates (100 ml/min) responses to hypocapnia were small, whereas at high flow rates (400 ml/min) responses were large. The PC50 (defined as the CO2 concentration required to produce a 50% increase in Rp above baseline Rp established on 5% CO2) at 400 ml/min (1.73%) was significantly larger than that at 100 ml/min (0.38%). We also directly measured the relationship between Rp and flow rate with 5% CO2 (normocapnia) or 1% CO2 (hypocapnia) delivered into the wedged segment. Increases in normocapnic flow caused small but significant decreases in Rp. In contrast, increases in hypocapnic flow from 100 to 400 ml/min caused a 108% increase in Rp. Thus the response to hypocapnia is augmented by increasing flow rate. This interaction can be explained by a simple model that considers the effect of local ventilation-perfusion ratio and gas mixing on the local CO2 concentration at the site of peripheral airway contraction.

Turbulence Measurements in a Centrifugal Pump With a Synchronously Orbiting Impeller

1991 ◽  
Author(s):  
Ronald D. Flack ◽  
Steven M. Miner ◽  
Ronald J. Beaudoin
Keyword(s):  
Centrifugal Pump ◽  
Reynolds Stress ◽  
Flow Rate ◽  
Cross Product ◽  
Design Flow ◽  
Low Flow ◽  
Rate Variation ◽  
Flow Rates ◽  
The Individual ◽  
Design Flow Rate

Turbulence profiles were measured in a centrifugal pump with an impeller with backswept blades using a two directional laser velocimeter. Data presented includes radial, tangential, and cross product Reynolds stresses. Blade to blade profiles were measured at four circumferential positions and four radii within and one radius outside the four bladed impeller. The pump was tested in two configurations; with the impeller running centered within the volute, and with the impeller orbiting with a synchronous motion (ε/r2 = 0.016). Flow rates ranged from 40% to 106% of the design flow rate. Variation in profiles among the individual passages in the orbiting impeller were found. For several regions the turbulence was isotropic so that the cross product Reynolds stress was low. At low flow rates the highest cross product Reynolds stress was near the exit. At near design conditions the lowest cross product stress was near the exit, where uniform flow was also observed. Also, near the exit of the impeller the highest turbulence levels were seen near the tongue. For the design flow rate, inlet turbulence intensities were typically 9% and exit turbulence intensities were 6%. For 40% flow capacity the values increased to 18% and 19%, respectively. Large local turbulence intensities correlated with separated regions. The synchronous orbit did not increase the random turbulence, but did affect the turbulence in the individual channels in a systematic pattern.

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